1. Field of the Invention
The present invention relates to an image display device including a liquid crystal panel and a transparent protective plate, or front panel, with a bonding material therebetween, wherein the liquid crystal panel is “voltage-controlled” to selectively transmit light from a backlight to display an image.
2. Description of the Related Art
In liquid crystal image display devices such as liquid crystal TVs, conventionally an image is displayed by applying a voltage to the liquid crystal layer while backlighting it in such a way that light of varying intensity emerges from the layer and passes through the color filter so that a desired color and intensity of light emerges from each pixel of the filter.
These image display devices include a backlight unit, a liquid crystal panel including the liquid crystal layer, etc., and a transparent protective plate, or front panel, for protecting the front surface of the liquid crystal panel. An elastomer (or elastic polymer) is used as a bonding material to bond the liquid crystal panel and the protective plate together. However, the prepolymeric precursor of the elastomer is a syrupy liquid with a low viscosity, meaning that it may spread to members adjacent to the liquid crystal panel if the bonding operation takes time.
JP-A-2002-287119 discloses a liquid crystal display device in which a silicone-based nonadhesive sheet having rubber-like elasticity is interposed between the liquid crystal display panel and the transparent protective plate, or front panel, such that one surface of the sheet is in close contact with the liquid crystal display panel and the other surface is in close contact with the transparent protective plate. It also discloses optimum surface roughness values, optimum rolling ball tack values, etc. for the surfaces of the silicone-based sheet. (See paragraphs [0020], [0023], [0030], [0064], etc.) On the other hand, JP-A-2007-041534 discloses that in an image display device the elastomer region (or bonding material) may spread to members adjacent to the panel (see paragraphs [0070], [0071], [0079], etc.).
Since, as described above, the prepolymeric precursor of the elastomer has a low viscosity, it may spread and adhere to the cut edges of the polarizing plates, etc. of the liquid crystal panel and to members adjacent to the liquid crystal panel if the bonding operation takes time.
If the prepolymer comes into contact with the cut edges of the polarizing plates, it may penetrate through the triacetyl cellulose (TAC) material making up the polarizing plates since triacetyl cellulose has large intermolecular spaces. This may lead to expansion of the polarizing plates. Further, iodine in the polarizing plates may leach out, resulting in reduced performance of the plates.
If the prepolymeric precursor of the elastomer contacts the conductive adhesive for bonding the LCD driver ICs, etc. to the glass substrates of the liquid crystal panel, the adhesive may swell resulting in poor adherence and conductivity.
Further, if the prepolymeric precursor of the elastomer comes into contact with the silicone coating agent for sealing the liquid crystal layer and the front and rear glass substrates of the liquid crystal panel (the liquid crystal layer being sandwiched between these glass substrates), the silicone coating agent may swell and may, at least to some extent, lose its sealing properties. This may cause the prepolymer to penetrate into the liquid crystal layer, resulting in the liquid crystal panel being unable to attain the desired performance.
The above JP-A-2007-041534 mentions that, in order to prevent the elastomer region from extending to the members adjacent to the liquid crystal panel, it is necessary to fully light cure the prepolymeric precursor of the elastomer.
The present invention has been devised in view of the above problems. It is, therefore, an object of the present invention to provide an image display device having a configuration that allows the device to be manufactured in such a way as to prevent unwanted spread and penetration of the prepolymeric precursor of the elastomer in its liquid crystal panel and thereby prevent the expansion and degradation of the members adjacent to the panel, which leads to an improvement in the performance of the image display device.